This invention generally relates to laser eye surgery devices, systems, and methods. In particular embodiments, the invention provides techniques for selectively altering refractive properties of corneas having regular and/or irregular optical defects, often by directing energy into the stroma.
Laser eye surgery systems and methods are now used to correct defects in vision, often using a technique known as ablative photodecomposition. In general, this technique applies a pattern of laser radiation to an exposed corneal tissue so as to selectively remove and resculpt the cornea. The pattern of laser energy often includes a series of discrete laser pulses from an excimer laser, with the locations, sizes, and/or numbers of pulses of the pattern being calculated to achieve a desired volumetric resculpting of the cornea, and to thereby create enhanced optical properties or treat optical defects.
Many patients suffer from optical defects which are not easily treated using standard glasses and contact lenses. Glasses and contacts often treat only regular or spherical and cylindrical refractive errors of the eye. Wavefront diagnostic techniques have been developed to measure irregular refractive errors, and these techniques have proven highly useful in determining customized refractive prescriptions for these patients. The flexibility of laser photorefractive decomposition offers hope to these patients, as this technique can be used to resculpt the eyes to correct both regular and irregular refractive errors. By combining laser eye surgery techniques with wavefront diagnostic approaches, it is often possible to achieve visual acuity measurements of 20/20 or better for many patients.
Early laser eye surgery treatments often involved the removal of the epithelial layer before changing the shape of the underlying corneal tissue. The epithelial layer tends to regrow, whereas volumetric resculpting of the underlying stroma can provide long-lasting effects. Corneal resculpting techniques involving mechanical abrasion or laser ablation of the epithelial layer so as to expose the underlying stroma for volumetric photoablative decomposition are often referred to as photorefractive keratectomy (“PRK”), and PRK remains a good option for many patients. In the last several years, alternative techniques involving formation of a flap of corneal tissue (including the epithelial layer) have gained in popularity. Such techniques are sometimes popularly referred to “flap-and-zap,” or laser in situ keratomileusis (“LASIK”). LASIK and related variations often have the advantage that vision can be improved within a few hours (or even minutes) after surgery is complete. LASIK flaps are often formed using mechanical cutting blades or microkeratomes, and the flap of epithelial tissue can be temporarily displaced during laser ablation of the stroma. The flap can reattach to the underlying stroma quite quickly, and the patient need not wait for epithelial tissue regrowth to experience the benefits of laser resculpting, so that these procedures are safe and highly effective for many patients.
A variety of alternative refraction altering techniques have also been proposed. In particular, focusing of femtosecond laser energy within the stroma so as to ablate a volume of intrastromal tissue has been proposed. By scanning the focal spot within an appropriate volume of the stromal tissue, it might be possible to vaporize the volume so as to achieve a desired refractive alteration. Despite possible advantages of intrastromal volumetric ablation techniques, these approaches have not yet gained the popularity of LASIK and/or PRK. Intrastromal femtosecond ablation techniques have, however, begun to gain popularity as a method for incising the cornea so as to form the flap of corneal tissue in LASIK and related procedures. Unfortunately, this combined approach often involves the use of both a fairly expensive intrastromal femtosecond laser for incising the corneal tissues, and then an excimer laser for resculpting the exposed stroma. The combined use these two separate, fairly complex and/or expensive laser systems may limit the acceptability and benefits of these new refractive laser eye surgery techniques.
In light of the above, it would generally be desirable to provide improved devices, system, and methods for laser eye surgery. It would be particularly desirable to expand the capabilities of lasers and allow their use for both incising and refractively altering the eye. It would be particularly desirable if such improved devices were suitable for correction of regular refractive errors and a irregular refractive alterations (such as correcting an irregular refractive error of the eye), ideally without having to resort to two separate laser systems.